The present invention relates to an audio processing method, audio processing apparatus, and recording and reproduction apparatus, which, in an apparatus such as a VTR apparatus for business use, 6-mm tape recorder apparatus, or the like, arranged to output a sound whose pitch has changed in proportion to the reproduction speed, enables a sound, whose pitch is normal regardless of the reproduction speed, to be output when reproducing the recorded sound at this given reproduction speed. Particularly, the invention concerns an audio processing method, audio processing apparatus, and recording and reproduction apparatus, which, when applied to a VTR apparatus, enables the production of a high quality of sound that matches with a wanted reproduction speed and that is synchronized with the image.
In general, in a case where reproducing at a given speed a sound that has been recorded in an analog recording medium such as a magnetic tape, the pitch of the sound is also changed in proportion to this reproduction speed.
Also, regarding a VTR apparatus for business use, recording of both an image and a sound has in recent years been performed predominantly by the use of a digital system. However, regarding the output of a sound, for the sake of increasing the efficiency of the editing operation, a sound whose pitch has changed is output in proportion to the reproduction speed as in the case of a VTR apparatus of analog system.
Meanwhile, regarding a VTR apparatus, although an image has hitherto been changeable speed reproduced, there has hitherto existed no VTR apparatus that has the function of, while synchronizing a sound with the changeable speed reproduced image, correcting the pitch of the sound to a normal level.
Also, if imposing a limitation on means for correcting the pitch of the sound, there is known a pitch shifter (pitch changer) which has been presently being used in a xe2x80x9ckaraokexe2x80x9d apparatus or the like. However, if using such a pitch shifter in the correction of the pitch in the above-described VTR apparatus, when the object sound is a human voice or the correction range therefor is wide, such as, for example, when restoring to the original pitch the sound whose pitch has been lowered 1 octave as in the case of a xc2xd time speed reproduction, there existed the problem with the quality of the sound, such as the problem that a large amount of distortion or echo feeling follows the corrected sound.
As will be understood from the above-described problems, when correcting a change in the sound pitch, if considering the quality of broadcasting, there has hitherto existed no suitable apparatus. Namely, when performing slow reproduction of a VTR apparatus that is used in, for example, broadcasting, there was the problem that it was impossible to use the sound that had been reproduced simultaneously with the reproduction of the image excepting a case where use was made of a non-realistic sound whose pitch had been intentionally changed.
The present invention has been made in view of the above-described problems and has an object to provide an audio processing method, audio processing apparatus and recording and reproduction apparatus which take in a sound which has been changeable speed reproduced within a practical use range of changeable speed as when having reproduced at a speed that is xc2xd time, or 2 times, higher and whose pitch has changed, and which, while the clearness of the sound is being maintained as is, enables the pitch of the sound to be restored to its original level within a range of xc2x11 octave or so in a state where the sound is synchronized highly accurately with the image.
To achieve the above object, according to an audio processing method as described in claim 1, the gist is that, in an audio processing method of, when reproducing, at a reproduction speed different from that at which an audio signal has been recorded in a recording medium, the audio signal on the recording medium, adjusting the pitch of the reproduced audio signal, wherein a sampling frequency fi, which is used when performing A/D conversion of the audio signal that has been reproduced from the recording medium at a changeable speed ratio r with respect to a normal reproduction speed to thereby produce audio data, and a sampling frequency fo, which is used when performing, after having performed digital signal processing on the audio data, D/A conversion thereof to thereby produce an audio signal, are respectively set so that these frequencies and the changeable speed ratio r may satisfy prescribed conditions.
According to an audio processing method as described in claim 2, the gist is that, in the audio processing method as described in claim 1, when performing digital signal processing on the audio data that has been obtained by performing A/D conversion, at the sampling frequency fi, of the audio signal that has been reproduced from the recording medium at the changeable speed ratio r, the digital signal processing comprising the steps of: performing a series of processes of performing analysis processing on the attribute of the audio data, dividing as the next step the audio data into blocks each having a prescribed time width according to data that has been obtained through the performance of the analysis processing and if necessary performing interpolation or thinning of the audio data in units of a block to thereby make a time length of the audio data if necessary 1/r time greater and thereby produce output audio data, and thereafter performing D/A conversion of the output audio data at the sampling frequency fo, to thereby produce an audio signal.
According to the audio processing method as described in claim 3, the gist is that, in the audio processing method as described in claim 1, as the prescribed conditions, when the sampling frequencies fi and fo and the changeable speed radio r satisfy the relationship of fi/fo=r, there is used the sampling frequency fi which is represented by an expression fi=rxc2x7fo; and when the sampling frequencies fi and fo and the changeable speed ratio r are in the relationship of fi/foxe2x89xa0r, there is used the sampling frequency fi that is represented by an expression fi=rxc2x7fo/c that includes a sampling frequency conversion coefficient c.
According to the audio processing method as described in claim 4, the gist is that, in the audio processing method as described in claim 2, as the prescribed conditions, when the sampling frequencies fi and fo and the changeable speed radio r satisfy the relationship of fi/fo=r, there is used the sampling frequency fi which is represented by an expression fi=rxc2x7fo; and when the sampling frequencies fi and fo and the changeable speed ratio r are in the relationship of fi/foxe2x89xa0r, there is used the sampling frequency fi that is represented by an expression fi=rxc2x7fo/c that includes a sampling frequency conversion coefficient c.
According to the audio processing method as described in claim 5, the gist is that, in the audio processing method as described in claim 4, when performing digital signal processing on the audio data that has been obtained by performing A/D conversion, at the sampling frequency fi, of the audio signal that has been reproduced from the recording medium at the changeable speed ratio r, the digital signal processing comprising the steps of: monitoring time data of the audio signal read out from the recording medium and time data of the output audio data that has been obtained through the performance of the series of processes to thereby correct time non-coincidence that occurs between the audio signal and the output audio data.
According to the audio processing apparatus as described in claim 6, the gist is that, in an audio processing apparatus for, when reproducing, at a reproduction speed different from that at which an audio signal has been recorded in a recording medium, the audio signal on the recording medium, adjusting the pitch of the reproduced audio signal, the audio processing apparatus comprising: A/D conversion means (3) for performing A/D conversion, at a sampling frequency fi, of the audio signal that has been reproduced from the recording medium; analysis processing means (5) for performing analysis processing on audio data that has been obtained by the A/D conversion according to the attribute thereof; block data division means (6) for dividing the audio data into block units each having a prescribed time width according to data that has been obtained by the analysis processing; output audio data production means (11) for performing a series of processings of performing interpolation or thinning processing on the audio data in divided block units if necessary to thereby make data length thereof 1/r greater and thereby produce output audio data; audio output means (12) for performing D/A conversion, at a sampling frequency fo, of the thus-produced output audio data to thereby output a sound synchronized with an image; and sampling frequency setting means for setting the respective sampling frequencies fi and fo so that the sampling frequency fi used when performing A/D conversion, the sampling frequency fo used when performing D/A conversion of the audio data to thereby produce an audio signal, and the changeable speed radio r may satisfy prescribed conditions.
According to the audio processing method as described in claim 7, the gist is that, in the audio processing apparatus as described in claim 6, as the prescribed conditions that are set by the sampling frequency setting means, when the sampling frequencies fi and fo and the changeable speed radio r satisfy the relationship of fi/ fo=r, there is used the sampling frequency fi which is represented by an expression fi=rxc2x7fo; and when the sampling frequencies fi and fo and the changeable speed ratio r are in the relationship of fi/ foxe2x89xa0r, there is used the sampling frequency fi that is represented by an expression fi=rxc2x7fo/c that includes a sampling frequency conversion coefficient c.
According to the audio processing apparatus as described in claim 8, the gist is that, in the audio processing apparatus as described in claim 7, the output audio data production means (11) comprises means for monitoring time data of the audio signal read out from the recording medium and time data of the output audio data that has been obtained through the performance of the series of processes to thereby correct time non-coincidence that occurs between the audio signal and the output audio data.
According to the recording and reproduction apparatus as described in claim 9, the gist is that this apparatus includes the audio processing apparatus according to claim 6.
According to the recording and reproduction apparatus as described in claim 10, the gist is that this apparatus includes the audio processing apparatus according to claim 7.
According to the recording and reproduction apparatus as described in claim 11, the gist is that this apparatus includes the audio processing apparatus according to claim 8.
As has been described above, according to the present invention, in an audio processing method of, when reproducing, at a reproduction speed different from that at which an audio signal has been recorded in a recording medium, the audio signal recorded in the recording medium, adjusting the pitch of the reproduced audio signal, a sampling frequency f1, which is used when performing A/D conversion of the audio signal that has been reproduced from the recording medium at a changeable reproduction speed ratio r with respect to a normal reproduction speed to thereby produce audio data, and a sampling frequency fo, which is used when performing, after having performed digital signal processing on the audio data, D/A conversion thereof to thereby produce an audio signal, are respectively set so that these frequencies and the changeable reproduction speed r may satisfy prescribed conditions. As a result of this, the invention takes in a sound which has been changeable speed reproduced and whose pitch has changed within a practical use range of changeable speed as when having reproduced at a speed that is xc2xd time, or 2 times, higher, and , while the clearness of the sound is being maintained as is, enables the pitch of the sound to be restored to its original level within a range of xc2x11 octave or so in a state where the sound is synchronized highly accurately with the image.
Also, the circuit of the invention can be constructed by adding merely a small number of circuits to the circuits that are conventionally employed.